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DS18b20 with a NPT threaded housing

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A few years ago I was able to purchase a few pre-fabricated DS18b20 in a 1/8 NPT threaded probe.

Does anyone know where, in the United States, I can economically purchase more? I can't seem to find anyone making or selling them (probably not using the right key words in my google searches).
 

Pommie

Well-Known Member
Most Helpful Member
Sparkfun do a sealed unit that you might be able to epoxy into a fitting. See Here.

Mike.
 
The problem with putting the waterproof sensors in a thermowell, is the size. The waterproof sensor is already large enough (ie., right amount of thermal mass). Once you add a thermowell large enough to accommodate the waterproof sensor, a lot more (thermal) mass is added.

I tried alibaba. Lots available, but I did not see anything in the US or economical enough to order and ship from overseas.

The one from aliexpress may work, but what is a G1/2 thread? 1/2" NPT?
 
The problem with putting the waterproof sensors in a thermowell, is the size. The waterproof sensor is already large enough (ie., right amount of thermal mass). Once you add a thermowell large enough to accommodate the waterproof sensor, a lot more (thermal) mass is added.

I tried alibaba. Lots available, but I did not see anything in the US or economical enough to order and ship from overseas.

The one from aliexpress may work, but what is a G1/2 thread? 1/2" NPT?
http://www.ring-plug-thread-gages.com/PDChart/G-series-Fine-thread-data.html
 
The one from aliexpress may work, but what is a G1/2 thread? 1/2" NPT?
Thanks for the link, that started me in direction of finding the difference. (I either don't see the listing on the site for the NPT or it isn't there). Further google search revealed 'G' or BPST has a larger taper than NPT (60 vs 55 degrees). I'm thinking I'm out-of-luck in the US trying to find (economical) BPST threaded fittings, not to mention the one-off factor they would be.
 

Superdat

Member
Hi
Is DS18B20 a must? A quick search on Ebay(UK) shows K type thermocouples available with 1/8NPT.
All depends what you are trying to do.
 
Yes, because (a) I can bus them together, (b) reduce the number of I/O (mostly input) connections required, (c) as aforementioned I already have some in use.
 

Superdat

Member
Ok
What is your intended usage? Also what temperature range are you looking for?
I just checked the sealed units that I get via ebay, they are 6mm diameter (probably the same as the ones suggested by Pommie) so they would just fit inside a 1/8 npt thread but the wall thickness wouldn't be much. A solid wall thickness of about 1.25mm (8.5-6)/2)+thread depth so about 2mm with the thread.
I was thinking engineering plastic like acetal to make an adapter but it depends on the application and how much mechanical strength is needed.
Metal migh be better, there wouldn't be much metal either, especially if you made the nut size as small as possible so thermal mass may not be a big issue.
You would most likely need to make the adapter yourself, do you have a lathe? If not rod a drill and a die but that's going to be a lot of work.
 
Though I don't see how this is relevant to finding a source for a DS18B20 sensor pre-mounted in NPT threaded housing; I need to measure additional points inside a fluid filled pipe up to 30-50 psig and between 50 and 200 degrees F.

I am fairly mechanically included and have a lot of tools, but trying to make a thermowell is well beyond the tools and materials I have access to. You would need a piece of steel rod 1/2" in diameter with the section that is not threaded, less than 0.350" to pass through the female fitting. Then you would need to drill the 0.350" section out with a 0.250" drill bit without breaking through the side of the 0.050" thick wall (0.350-0.250 =0.1 diameter = 0.050 radius) you are trying to leave behind.

I am pondering if the compression fitting has enough strength to hold the probe in at 50 psig and if the probe would be resuable or if the compression fitting will make it one time use (becuase of damage to the sensor housing).
 

jpanhalt

Well-Known Member
Most Helpful Member
I don't understand why you can't get an inexpensive NTC sensor or any other type with the proper thread and thermowell, drill it out, and insert your digital sensor (in the bare 3-pin version) as shown in this link (copied from above): https://forum.reveltronics.com/viewtopic.php?t=44

One could probably do it without a lathe, but it would be quite simple to do with a lathe. Do you have a metal cutting lathe in your shop?

John
 

Superdat

Member
Though I don't see how this is relevant to finding a source for a DS18B20 sensor pre-mounted in NPT threaded housing; I need to measure additional points inside a fluid filled pipe up to 30-50 psig and between 50 and 200 degrees F.

I am fairly mechanically included and have a lot of tools, but trying to make a thermowell is well beyond the tools and materials I have access to. You would need a piece of steel rod 1/2" in diameter with the section that is not threaded, less than 0.350" to pass through the female fitting. Then you would need to drill the 0.350" section out with a 0.250" drill bit without breaking through the side of the 0.050" thick wall (0.350-0.250 =0.1 diameter = 0.050 radius) you are trying to leave behind.

I am pondering if the compression fitting has enough strength to hold the probe in at 50 psig and if the probe would be resuable or if the compression fitting will make it one time use (becuase of damage to the sensor housing).
It is relevent, if I'd known that, I wouldn't have suggested engineering plastic, and jpanhalt probably wouldn't have suggested glueing a sensor inside an adaptor which is what I was thinking too.
A compression fitting might crush the tube on the DS18B20, but if it doesn't it should hold. Mains water is about 40-45 in the UK and compression joints hold that OK.
At 50psi and 200F you don't want it coming out so the olive needs to be tight. That means it won't come off easily. Almost all of the 15mm olives and 22/28mm I've ever undone have "biten into the tube, only very lightly tightened ones can be encouraged to come off.
Ebay(US) have a Chinese 6mm compression to 1/8npt but it's $4, you might get one cheaper at your local gas/plumbing store.
If that doesn't work, I would 2nd Jpanhalt's idea of using an NTC thermistor, they are tiny and would easily fit inside a 1/8 npt.
If you could get hold of a 1/8npt solid plug or threaded rod, you would only need to drill a hole of about 1/16" part way into the plug, then seal it in.
They are quite accurate and the circuit is simple, it needs one ADC.
 
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